Rectifying circuits that include Schottky diodes are often used as (a) external components to power management Integrated Circuit (PMIC) designs, (b) Rectifier in a bootstrap circuit, (c) a free wheeling diode in a boost or (d) a buck convertor in asynchronous switch mode power supply (SMPS).
A Schottky diode that is integrated on a single silicon chip (die) is preferable to a discrete Schottky diode due to its lower cost and size and reduced wire parasitic inductances. Integrated Schottky diodes however may inject current to the substrate and disturb the circuits performance. Such a Schottky diode may include an N-well that contacts a Schottky conducting pad.
In order to suppress leakage current of Schottky diodes, the Rectifying circuit also includes a guard ring. The guard ring includes a guard conducting pad that is contacted by a P+ region. The P+ region is surrounded by a P well. The P well contacts the N well.
The P well and the N well form a PN diode.
The PN diode and the Schottky diode are electrically coupled to each other in parallel.
In reverse bias the guard ring assists in depleting the semiconductor in proximity to a metal Anode of the switching circuit thus reducing the local fields in the metal semiconductor interface and hence increasing the breakdown voltage and lowering the leakage current.
When the PN and the Schottky diodes are in forward bias at above 0.6V the PN diode opens and injects minority carriers into the lightly doped N well located above a substrate. This minority charge slows down the turn-off process of the Rectifying circuit also referred as the reverse recovery charge. It also may diffuse through the N well to the substrate of the Rectifying circuit thus causing high substrate currents. These currents may interfere with the analog control circuitry on chip and cause circuit failure.
There is a growing need to provide a fast and highly efficient Rectifying circuit that includes a Schottky diode.